As an image forming method employing an electrophotographic toner (hereinafter occasionally referred to as toner), heretofore, from the viewpoint of simplicity as well as convenience, a dry development system, which uses a magnetic brush and the like, has been employed. In said development system, an electrostatic latent image is formed on the surface of a photoreceptor and said electrostatic latent image is subjected to toner development, employing a magnetic brush and the like. The resulting toner image is then transferred onto a transfer material employing means such as electrostatic transfer and the like, and finally the toner is fixed onto the transfer material, employing common means such as a heated roll and the like to form long lasting images. Any toner, which is not transferred and remains on the photoreceptor, is removed as waste toner, employing conventional means such as a cleaning blade and the like.
In recent years, image forming methods, which utilize an electrophotographic system, have been widely employed as a hard copy output system, especially for printers, and the like.
In such a system, in order to obtain high image quality, a decrease in the diameter of toner particles is demanded. As the diameter of toner particles decreases, the surface area of the toner increases. Thus, moisture adsorption and the like increases, and variation of chargeability increases in response to variations of ambient conditions in which said toner is employed. As a result, it is difficult to consistently form images.
Further, it is known that an electrophotographic toner is provided with chargeability as well as fluidity by adding external additives such as fine inorganic particles, and the like, to colored particles. As such fine inorganic particles, for example, Japanese Patent Publication Open to Public Inspection Nos. 59-52255, 62-129861, 6-11886, 6-75430, 7-230179, as well as others, describe various items on hydrophobic titanium dioxide which minimizes the influence of ambient conditions under which the toner is employed.
However, when toner particles having a small diameter are employed for an extended period of time, fine inorganic particles are occasionally buried in the surface of colored particles. Therefore, at present, it is impossible to consistently maintain the desired effects of such fine inorganic particles.
Further, recently, from the viewpoint of minimizing waste, a recycling system, in which waste toner collected by a cleaning means is reused for subsequent development, has received great attention. When said waste toner is reused through recycling, a mechanism, in which said toner is recovered and conveyed from the cleaning section to the development section, is specifically provided. During conveyance and the like, the toner is subjected to stress. As a result, the fine inorganic particles tend to be buried in colored particles. The surface state of toner, comprising the colored particles into which fine inorganic particles are buried, is greatly affected by the fine inorganic particles. As a result, the amount of adsorbed moisture largely varies depending on the variations of the ambient conditions. Thus, when the ambient conditions, under which the toner is employed, vary, the variation of chargeability is exaggerated, and the problem of variation of image density as well as background stain occurs.
Due to that, desired is a toner which is not subjected to variation of ambient conditions, but can maintain consistent image quality for an extended period of time.